The development of absorbent articles for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins is the subject of substantial commercial interest. The ability to provide higher performance absorbent articles is primarily contingent on the ability to develop highly absorbent cores or structures that can acquire, distribute, and store large quantities of discharged body fluids, such as urine.
Open-celled polymeric foams are one example of absorbent materials capable of acquiring, distributing, and storing large quantities of discharged body fluids. Absorbent articles containing such foams can possess desirable wet integrity, can provide suitable fit throughout the entire period the article is worn, and can minimize changes in shape during use (e.g., uncontrolled swelling, bunching). In addition, absorbent articles containing such foam structures can be easier to manufacture on a commercial scale. For example, absorbent diaper cores can simply be stamped out from continuous foam sheets and can be designed to have considerably greater integrity and uniformity than absorbent fibrous webs. Such foams can also be prepared in any desired shape, or even formed into single-piece diapers.
Particularly suitable absorbent foams for high performance absorbent articles such as diapers have been made from High Internal Phase Emulsions (hereafter referred to as "HIPE"). See, for example, U.S. Pat. No. 5,260,345 (DesMarais et al), issued Nov. 9, 1993 and U.S. Pat. No. 5,268,224 (DesMarais et al), issued Dec. 7, 1993, hereby incorporated herein by reference. These absorbent HIPE foams provide desirable fluid handling properties, including: (a) relatively good wicking and fluid distribution characteristics to transport the imbibed urine or other body fluid away from the initial impingement zone and into other regions of the foam structure to allow for subsequent gushes of fluid to be accommodated; and (b) a relatively high storage capacity with a relatively high fluid capacity under load, i.e. under compressive forces.
When formed into sheets or webs, these HIPE absorbent foams are also sufficiently flexible and soft so as to provide a high degree of comfort to the wearer of the absorbent article; some can be made relatively thin until subsequently wetted by the absorbed body fluid. See also U.S. Pat. No. 5,147,345 (Young et al), issued Sep. 15, 1992 and U.S. Pat. No. 5,318,554 (Young et al), issued Jun. 7, 1994, which discloses absorbent cores having a fluid acquisition/distribution component that can be a hydrophilic, flexible, open-celled foam such as a melamine-formaldehyde foam (e.g., BASOTECT made by BASF), and a fluid storage/redistribution component that is a HIPE-based absorbent foam.
Currently, HIPE foam production is batch processed by curing (polymerizing) a high internal phase emulsion in large tubs or vats. Once cured, the resulting block of material is a water-filled, open-celled foam. By water-filled is meant that the porous structure is substantially filled with the residual water phase material used to prepare the HIPE. This residual water phase material (generally an aqueous solution of electrolyte, residual emulsifier, and polymerization initiator) is typically about 96-99% by weight of the cured HIPE foam. The cured foam block is preferably substantially cylindrical in shape, the shape being determined by the shape of the tub or vat, which is essentially a mold. In a typical batch process, the cured, water-filled foam block is generally cylindrical in shape, approximately 40-60 inches in diameter, approximately 24 inches high, and weighs from 500-2000 pounds.
For use in absorbent articles as part of an absorbent core, the block of water-filled foam is formed into relatively thin sheets and dewatered. The polymerized HIPE foam is typically cut or sliced to provide a sheet thickness in the range from about 0.08 to about 2.5 cm. It is preferable that the polymerized HIPE foam be cut or sliced into sheet form prior to dewatering since sheets of polymerized HIPE foam are easier to process during subsequent treating/washing and dewatering steps.
It is also preferable that continuous webs of dewatered foam material be formed and be converted to roll stock, suitable for subsequent processing into absorbent cores in a continuous process. However, current methods of cutting or slicing a block of cured foam do not permit cutting substantially continuous webs or sheets of material. Due to the size, weight, and structural integrity of the water-filled, porous block after curing, forming continuous webs of uniform thickness is not economically practical or technically feasible. For example, the weight and structural integrity of the foam block requires it to be fully supported during any subsequent processing, including cutting or slicing continuous webs or sheets. Such a configuration does not lend itself to being cut by known slicing or cutting techniques.
Continuous webs of uniform thickness may be produced by cutting about the circumference of a cylindrical block. If, however, the block must be fully supported upon its cylindrical base, these techniques are not feasible since they require a vertical cutting blade, the ends of which should be supported above and below the block. There is no space for a blade support below the block, however, due to the necessary supporting platen or platform. A reciprocating blade supported only at the upper end, e.g., a "saber" saw, may be used, but such a blade still needs clearance at least equal to the stroke length below the material being cut. Therefore, since the size and weight of the block limits the practicable options for producing continuous webs to those involving slicing or cutting around its circumference, the technically feasible processing of continuous webs of material by conventional methods such as veneering, or cutting by use of conventional saws is limited.
An additional problem faced when trying to cut continuous webs from a generally cylindrical block of water-filled HIPE material is subsequent web handling to form roll stock of webs. Water-filled HIPE foam webs are preferably dewatered prior to winding into roll stock. Dewatering of the continuous web may be accomplished in a number of ways, including squeezing between a series of dewatering nip rollers, suction by way of vacuum conveyors, or drying by radiant or convection heat. In general, however, such web processing requires that the web be moving at a constant rate to provide reliable and repeatable drying results. Therefore, cutting or slicing a continuous web of water-filled HIPE foam from the perimeter of a cylindrical block is preferably accomplished as the block is rotating at a constant tangential velocity rather than a constant angular velocity.
Accordingly, it would be desirable to be able to form continuous webs of material from a monolithic block of material.
Additionally, it would be desirable to be able to form continuous webs of material from a monolithic block supported upon a platen or platform.
Additionally, it would be desirable to be able to form a continuous web of water-filled HIPE foam material from a cured block of foam material.
Further, it would be desirable to be able to form continuous webs of foam material in an automated process such that webs of uniform thickness are produced at a uniform linear velocity.